The present disclosure generally relates to a method of forming semiconductor structures, and more particularly to a method for low temperature selective epitaxy of a semiconductor alloy including at least silicon and germanium employing a high order silane precursor.
High order silanes refer to SinH2n+2, in which n is an integer greater than 3. Chemical vapor deposition processes employing a high order silane can provide higher deposition rates and lower deposition temperatures compared to chemical vapor deposition processes employing silane or disilane. Gas phase reaction that forms silicon particulates in the gas phase is responsible for such high deposition rates and low deposition temperatures of chemical vapor deposition processes employing a high order silane.
For epitaxial silicon deposition processes, chemical vapor deposition processes employing a high order silane are not suitable because the gas phase reaction that is responsible for enhanced growth rates is also responsible for formation of gas phase silicon particulates and incorporation into a deposited film as a defect that degrades the crystallinity of the deposited film. In other words, the deposited silicon film becomes embedded with polycrystalline silicon grains and epitaxial alignment with an underlying single crystalline material is lost in the deposited film. For this reason, high order silanes are avoided in epitaxial deposition processes for silicon.